10th_11th_lecture_Ch3_9_21&22_2011

10th_11th_lecture_Ch3_9_21&22_2011 - Which of the...

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Which of the following is not relevant when evaluating the stability of a conjugate base from a Bronsted acid? 1 2 3 4 0% 0% 0% 0% 1. Electronegativity 2. Resonance 3. Inductive effect 4. Octet rule
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More review for ch1 and 2. HA H + + A - HB H + + B - The more stable the –ve charge is (either A - or B - ), the stronger the acid is (either HA or HB corresponding) When comparing the stability of A - and B - , octet rule is not relevant. (think about it) The above is for Bronsted acid only. How come for Lewis acid and base, octet rule will matter?
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Which of the following is the best representation for benzene? 1 2 3 0% 0% 0% a b c 1. a 2. b 3. c
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Resonance structures: Different resonance structures actually are for understanding and representing the one hybrid structure that actually exist. So people talk about “the resonance structure that contribute most to the hybrid”, this structure is the most stable one. Some resonance structure may break the octet rule.
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Draw the product as the result of the flow of the electrons show below.
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Did you get it right? 1 2 0% 0% 1. Yes, I got it right. 2. No, I did not.
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Draw the product as the result of the flow of the electrons show below.
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Did you get it right? 1 2 0% 0% 1. Yes, I got it right. 2. No, I did not.
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Draw the arrows on both of the structures to show how the resonance occur between these two structures.
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Did you get it right? 1 2 0% 0% 1. Yes, I got it right. 2. No, I did not.
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Chapter 3 Conformations (shape and movement) of Alkanes and Cycloalkanes
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• Three-dimensional shapes of molecules result from many forces. • A molecule may have several or many different shapes, called conformations , that ALL exist, but are in different populations. The exact populations for each depends on the energy, and thus are in equilibrium at room temperature The Shapes of Molecules
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• Conformations may interconvert rapidly • Molecular models are 3D objects that help us visualize the conformers • Representing 3D conformers in 2D is done with standard types of drawing Conformations of Ethane
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Sawhorse representations show molecules at an angle like in a molecular model • C-C bonds are at an angle to the edge of the page and all C-H bonds are shown Sawhorse Representations
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Newman projections show how the C-C bond would project end-on into the paper • Bonds to the front carbon are lines going to the center • Bonds to the rear carbon are lines going to the edge of the circle Newman Projections
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• The barrier to rotation between conformations in ethane is small (12 kJ/mol) • The most stable conformation of ethane has all 6 C-H bonds pointing away from each other ( staggered ) • The least stable conformation has all 6 C-H bonds as close as possible ( eclipsed ) - this is due to torsional strain Ethane's Conformations
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• The two bonds are anti when the angle between them is 180° Anti Relationships H H H H H H H H H H H H H H H H H H H H H H H H 180° 180°
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• The two bonds are gauche when the angle between them
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10th_11th_lecture_Ch3_9_21&22_2011 - Which of the...

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